Data centres with server farms are essential to the functioning of information handling systems in different applications and sectors in the modern economy. Generally, server farms in data centres include a large number of servers that consume power during operation to process and handle jobs or computational tasks. Energy efficiency, often defined as the ratio of job throughput to power consumption, is an important factor to consider when designing or operating server farms, as excessive power consumption in server farm may cause unnecessary greenhouse gas emissions and/or other environmental concerns. Driven by the green data centre initiative to facilitate a low carbon economy in the information age, there is a strong incentive for server farm operators to devise an optimal strategy in operating and managing server farms so as to conserve energy and maximize energy efficiency of server farms.